An aircraft comprises a large amount of equipment, of diverse nature, mechanical, hydraulic, electrical or electronic, whose proper operation is essential in the course of a flight.
To improve the degree of confidence accorded to this equipment, monitoring of its proper operation is undertaken, as often as possible, for each item. Monitoring generally comprises checking the fundamental parameters and automatic or semi-automatic tests of proper operation. Generally, a fault diagnosis is carried out and may lead to the emitting of fault messages.
A monitoring and alarm function makes it possible to detect a malfunction having an impact on the safety of the aircraft. A function of this type, also called “Flight Warning” in the art, is present on certain aircraft. A subfunction of the “Flight Warning”, generally, named “Flight Deck Effect” in the art, makes it possible to present these alarms to the crew, these alarms referring to cockpit effects that may be interpreted as anomalies by the pilot.
Additionally, a maintenance function is associated with the monitoring function in order to diagnose faults and store them.
It is known by the name of BITE function, derived from the abbreviation of the expression “Built In Test Equipment”.
The BITE function of an item of equipment is taken on by electronics which may be specific or shared with other functions of the item of equipment considered. This electronics performs the software processing required by the BITE function.
It comprises a more or less significant hardware part secured to the item of equipment, with, at the minimum, in this hardware part, a nonvolatile memory. Certain data are stored in the volatile memory, including the breaching of standards by the monitored parameters, the results of the tests, the fault diagnostic when it exists as well as the fault messages emitted. The fault messages of the BITE functions of the monitored equipment of an aircraft are addressed, by an airplane data transmission link, to a centralizer item of equipment placed aboard the aircraft so as to bundle together the various fault messages emitted.
Aboard recent aircraft, fault messages originating from the BITE functions of the various items of equipment are consultable from the flight deck. They are furthermore preprocessed, with a view to easing the task of crews and maintenance personnel, by a specialized central computer known by various terms such as CMC from the expression “Central Maintenance Computer” or else CFDIU from the expression “Centralized Fault Display Interface Unit”.
This central maintenance computer is accessible by the crew through an interface with keyboard and screen which may be that known by the abbreviation MCDU derived from the expression “Multipurpose Control Display Unit” but which may also be a portable computer of the PC kind attached by a disconnectable data link which does or does not utilize the airplane bus.
Its main function is to effect, in real time or at the end of a flight, a diagnostic of the general situation of the aircraft. This diagnostic is carried out on the basis of a summary of the fault messages received from the various items of equipment of the aircraft.
II also fulfils other functions such as:                correlation of the fault messages received with the alarms received at the flight deck level;        running of particular tests on the items of equipment, conducted on request, by an operator intervening from the keyboard-screen interface giving access to the central maintenance computer;        drafting of a “post-flight” report, known by various terms such as PFR or LLR for “Post Flight Report” or “Last Leg Report”. This report is, generally, carried out for the maintenance teams on the ground.        
The latter function which consists in providing a “post-flight” report makes it possible to ease the work of the ground maintenance crew. It comprises a log of the fault messages emitted by the various items of equipment of the aircraft and alarms presented to the crew as well as the summary of the fault messages made as a last resort and more generally, all the information on the operating states of the equipment. The information featuring in this report results from automatic exploitation of the equipment fault messages or remarks by the crew.
The faults are generally correlated with the equipment failure probability. This failure probability is estimated on the basis of a reliability model and is stored in a static manner.
This correlation makes it possible to plan anticipated or preventive maintenance actions on the corresponding items of equipment.
The logical chain for deciding the maintenance actions results from the noting of a proven fault and then its location and finally a formulated diagnostic.
Additionally, more and more data are being monitored around avionics equipment, such as vibrations, electromagnetic and thermal signatures and other data which make it possible to reconstitute the immediate environment of the computer. These data do not systematically generate proven faults.
Certain monitoring systems analyse the error rate or the number of lost frames which make it possible to identify not a fault but a possible degradation of the wiring. It is considered that this monitoring and the analysis of the degradations of an item of equipment may lead to a prognosis being carried out on the airplane's data network.
A prognosis carried out on engines exists today. Prognoses are evaluated on certain items of equipment, notably those named ACMS, the acronym standing for Aircraft Condition Monitoring System. The engine parameters, such as the temperatures or vibrations, for example, are recovered and monitored. Certain breaches of thresholds (or overshoots), for example, make it possible to trigger alarms advocating intervention actions.
On the other hand, the monitoring of these fault generating degradations is not correlated with the functions of the system. No functional analysis is carried out on the basis of the degradations detected. Moreover, the degradation information is processed without considering the reliability model of the functions, and this could make it possible to provide a preventive maintenance report.
Moreover, the analysis of the degradations is not generalized to all the equipment and is not analysed jointly with the functional architecture of an aircraft.